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POWER PLANT ENGINEERING (REE-401) Ccccc UNIT-I

Unit-I: Hydro- plants- selection of site, elements of power plant, classification, water turbines, governor action,

hydro-, plant layout, pumped storage plants.

1.1INTRODUCTION: Hydro-electric power plants uses the associated with it. kinetic or potential of water to produce electrical (v) Access to site: The site should be easily accessible and it energy by electromechanical energy conversion phenomenon. should have transportation facilities. The motion of water provides it kinetic energy while potential (vi) Geological investigations: Geological survey is very energy is there due to the different levels of water between important to see the foundation rock for the dam and two points, called head. In both the cases water is collection other structures. It is an important factor to understand is necessary which is to be done by collecting it in lakes and that the land where we are going to construct hydro plant reservoirs at high altitudes which may be natural or manmade is capable to withstand the stress of such mega structures. constructions like artificial lake, ponds or dams. A hydro may be solve several problems like, power 1.4 ADVANTAGES: generation, comprising flood control, irrigation etc. A hydro- (i) No is required, therefore operating cost is low. electric power station cannot be located anywhere. The (ii) Large life span (about 50+ years). requirments to stablish it is more specific. Fristly there must (iii) No standby losses. be ample quantity of water available at sufficient head and (iv) These plants are more robust as compared to others. secondly a suitable site must be there. It requires an effective (v) Maintenance cost is low as compared to steam and civil engineering work, a hudge construction and a big capital plants. cost. (vi) Efficiency does not depend on its age. (vii) Its use helps in conservation of fossil . 1.2 WATER POWER: Water storage has potential energy. (viii) Few skilled workers are required to run the plant. When water drops through a height, its energy is able to (ix) In addition to power generation, multiple projects like rotate turbines which are coupled with alternators. By irrigation, flood control, navigation etc. are also served electromechanical conversion action this energy is converted at same time. into electrical energy. (x) Free from air pollution. From Bernoulli’s equation, the electrical power , P is given 0.736 1.5 DISADVANTAGES: by: P  Qwh kW 75 (i) High capital cost. where: Q = discharge in m3/sec (ii) These plants are dependent on water availability, so in w = density of water = 1000 kg/m3 a dry year, the power generation is very small. h = head in meters. (iii) Required large time to build. Another way is to represent this power is as: (iv) Proper supervision of dam is required.

0.736 P  Qwh kW; 1.6 CLASSIFICATION OF HYDRO-ELECTRIC 75 POWER PLANT: The classification of hydro-electric power (휂=overall efficiency of turbine alternator set). plant is based on: (1) Quantity of water available 1.3 SITE SELECTION: Following factors should be (2) Available load considered while selecting the site of a hydro power plant: (3) Nature of the load (i) Availability of Water: The river run-off data pertaining to many previous years should be analyzed to estimate of (1) Quantity of water available: According to this the plants the power potential of the project can be done. It decides may be divided into: the capacity of the plant. Also useful to setting up of (a) Run-off River plants without pondage peak load and avoid adequate spillways relief during the (b) Run-off River plants with pondage flood periods. (c) Reservoir plants. (ii) Water Storage: Water storage is necessary to maintain the availability of water throughout the year which may (a) Run-off River Plants Without Pondage: affected by the wide variation in rainfall during the year.  The plant uses water as it comes, there is no storage or (iii) Head of Water: In order to generate power, proper head pondage. of water is very important. An increase in head of water  There is no control on flow of water. So during periods reduces the capital cost of the plant by reducing the of high flows or low loads, water is wasted while during storage of water, handled by penstock, screens and lean flow periods, the plant capacity is very low. turbines.  Such sites are mainly used for irrigation or navigation (iv) Distance from the load centre: The site should not whereas the plant is only identical. locate far away from the load centre because this may (b) Run-off River Plants With Pondage: increase the cost of transmission line and the losses  In such sites pondage are used for storing the water

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which permits storage of water during the peak-off (c) High Head Plants: periods and use it during peak-off load.  Head is above 300 mtrs.  The firm capacity of the plant increases.  In such plants, all water is carried from the main  This type of plant is more reliable and its generating reservoir by a tunnel upto a surge tank and then to the capacity is less dependent on available rate of flow of power house in penstock. water.  For lower head Francis turbine is common but heads above 500 meters. Pelton turbines are used. (c) Reservoir plants:  These plants have a reservoir of such size as to permit DAM water storage from wet season to the next dry season. HEAD RACE  Water is stored behind the dam and is available to the SURGE plant with control as required. TANK  These plants having better capacity and works efficiently throughout the year. P  Most of the hydro power plants belong to this category. E POWER N S HOUSE T O C K (2) Available Head: Hydro power plants may be classified TAIL RACE as: (a) Low Head Plants, (b) Medium Head Plants, A High Head Plant (c) High Head Plants. (3) Nature Of The Load: On basis of nature of the load, plants may be divided as: (a) Low Head Plants: (a) Base-load Plants,  In such plants the water head is less than 30 mtrs. (b) Peak-load Plants,  Small dam is built across the river to provide the (c) Pumped storage plants for peak-loads. necessary load.  In such plants no surge tank is needed. (a) Base Load Plants:  The excess water is allowed to flow over the dam itself.  They are used to provide base load to the system.  Francis of Kaplan turbines are used.  Generally of high efficiency.  Supplies almost constant load throughout. HEAD  Operate on a high load factor. RACE DAM  Run-off river plants without pondage and reservoir plants POWER can be used as base load plants. HOUSE TAIL RACE (b) Peak-load Plants:  They are use to supply peak loads to the system.  Run-off river plants with pondage can be used as peak- A Low Head Plant load plants. (b) Medium Head Plants:  Reservoir plants with enough storage can be used either  In medium head plants, the water head is between 30 to as base-load plants or as peak-load plants as required. 300 mtrs.  Water is generally carried in open canals from main (c) Pumped Storage Plants For Peak-loads: reservoir to the fore-bay and then to the power house through the penstock. HEAD RACE  Generally Francis, Propeller and Kaplan turbines are D used. A HEAD RACE M PENSTOCK POWER HOUSE

D WITH PUMPS A E TAIL FOREBAY TAIL RACE H RACE

PENSTOCK POWER HOUSE

A Medium Head Plant Pumped Storage Hydro Electric Plant

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 They are used when the availability of water quantity is insufficient for generation. 1.7 LAYOUT OF A HYDRO-ELECTRIC POWER  A storage pond is built to store water at head and tail STATION: Figure shows a general layout of a hydro electric race. power plant with an artificial storage reservoir formed by  Head race water is fed to the turbine to generate constructing dam across a river. Water from the storage electrical energy and this water is stored in tail race reservoir is carried through penstocks or canals to the power which may be again pumped up to the head race when house. This water is used to rotate the turbine and after required through a centrifugal pump. passing through the turbines this water is discharged to the  The pumping back of water is done during off-peak tail race. The tail race is the channel which carries water away period. from the power house after it has passed through the turbine.  Such plants can only be operated in interconnected systems where other generating plants are also available.

DAM ENERGY LINE D

A PENSTOCK GENERATOR E H

S S

O REACTION R TUBE G

TAIL RACE

DRAFT TUBE

(a) DAM

IMPULSE TURBINE D

A PENSTOCK

E

H

S

S

O

R G

TAIL RACE NOZZLE

(b) General layout of a hydro-electric power plant.

1.8DIFFERENT COMPONENTS IN HYDROELECTRIC year by proper controls. PLANT: The following are the main components/stages of a (c) TRASH RACK: It prevents the entries of debris which hydroelectric plant: might damage the wicket gates and turbine runners of (a) RESERVOIR: Its purpose is to store water which may mean choking of nozzles of the turbine. It is made of be utilized to run the prime mover of the turbine to steel bars and is placed across the intake. produce electrical energy. A reservoir stores water (d) FOREBAY: It works as a regulating reservoir storing during rainy season and delivers it during the dry water temporarily when load on the plant is reduced season. and providing water for increasing load situation. It is (b) DAM: It provides a head to the water to be utilized in and enlarged body of water at the intake to store water the water turbine, which can be used throughout the temporarily to meet the hourly load fluctuations. It may

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be enlarged section of the canal or a pond. an impulse turbine are usually bucket-shaped so they (e) SURGE TANK: This is an additional storage space catch the fluid and direct it off at an angle or sometimes near the turbine, generally used in high head and even back the way it came (because that gives the most medium head plants when there is a considerable efficient transfer of energy from the fluid to the distance between the water source and turbine which turbine). In an impulse turbine, the fluid is forced to hit necessitates a long penstock. When the load on the the turbine at high speed. turbine decreases the surge tank provides space for holding water. Similarly when load on the turbine (b) REACTION TURBINES: In a reaction turbine, the increases it furnished additional water. blades sit in a much larger volume of fluid and turn (f) PENSTOCK: It provides a path for taking water from around as the fluid flows past them. A reaction turbine the intake work and fore-bay to the turbines. Penstocks doesn't change the direction of the fluid flow as may be classified as, the low pressure and high drastically as an impulse turbine: it simply spins as the pressure. fluid pushes through and past its blades. Wind turbines (g) SPILLWAY: Spillway is an arrangement to discharge are perhaps the most familiar examples of reaction excess water during floods. These should be so turbines. designed as to discharge the major flood water without damage to the dam but the same time maintain a (i) PELTON TURBINE: predetermined head. (h) POWER HOUSE: Power house is generally located at the foot of the dam and near the storage reservoir and HO RI responsible for power generation. CASING T ZO E SH N (i) PRIME MOVER: They are used to convert the kinetic CK A TA U FT L energy of the water into . Commonly B used prime movers are Pelton wheel, Francis/Kaplan/Propeller turbines. (j) TAIL RACE: It is required to discharge the water, leaving the turbine, into the river. GRADIENT RESERVOIR SPEAR SURGE TANK

M POWER A TUN D NEL HOUSE WATER JET

TAIL RACE PENSTOCK WATER FROM PENSTOCK Surge Tank & Pen Stock Pelton Turbine  This turbine work under large head and low quantity of 1.8 HYDRAULIC TURBINES: According to their action, water. the hydraulic turbines may be divided into two categories:  It is tangential flow impulse turbine. (a) Impulse turbines;  The pressure inside is atmospheric pressure, in which (b) Reaction turbines. the potential energy of water in the penstock is converted into kinetic energy in a jet of water issuing from nozzle.  From the nozzle, water comes out in the form of jet and strikes the buckets of the runner and causes the motion of the rotor.  After performing work, water discharges into tail race.  The rate of flow of water can be controlled by the movement of spear.  The rotor (or runner) is made of cast steel.  The buckets are bolted on the runner and made of cast iron, bronze or stainless steel. (a) Impulse Turbine (b) Reaction Turbine  For low head of water, Pelton wheel required a large diameter for the same output so it is not suitable for (a) IMPULSE TURBINES: In an impulse turbine, a heads below 200 m. fast-moving fluid is fired through a narrow nozzle at the turbine blades to make them spin around. The blades of

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(ii) FRANCIS TURBINE:  In these turbines negligible loss is occurred at low head  This turbine is an inward mixed flow reaction turbine and therefore uniform efficiency maintains at all loads. suitable for medium heads and medium flows.  It provides high speed as compared to other types of  In such turbines, the power is developed partly due to the turbines. velocity of water and partly due to difference in pressure acting on the front and back of the runner buckets. SLIDE VANES SHAFT  They are of large sizes and are generally of vertical type to effect economy in space.  The water, under pressure, enters the runner from guide vanes radially and discharges out of the runner axially.  In this turbine, water glides over the blade with a small and constant velocity and exerts pressure varying from maximum at the top to a small value at the bottom.  As the water passes over rotating blades of the runner

both pressure and velocity of water are increased causing D

R

A a reaction force driving the turbine. After doing work

F E

T

water is discharged to the tail race through the draft tube. L

S B

T

E A

 Francis runners for low heads may be of cast iron but U

D T

B

S A

heads above 100 m, cast iron or bronze is preferred. E

L

U J

B NOSE D

From Penstock A CONE

Kaplan Turbine RUNNER

1.9 GOVERNOR ACTION (GOVERNING OF TURBINES): The hydraulic turbines are directly coupled to electric generators. It is desired that speed of these generators should be constant irrespective of variations in the load. In order that the generator may always run at a constant speed the speed of the turbine runner must be maintained constant and this is usually done by regulating the flow of water passing through the runner in accordance with variations in the load. Stationary Vanes Scroll To perform such operation is called governing of turbines and it is done automatically by means of a governor. The most Adjustable common governors used with modern turbines is oil pressure governor. Guide vanes RUNNER

PENDULAM TO CLOSE or TO OPEN ACTUATOR MAIN LEVER

RIGID DISTRIBUTING Draft Tube FULCRUM VALVE FROM TAIL RACE TURBINE MAIN SHAFT Francis Turbine GEAR PUMP (iii) PROPELLER & KAPLAN TURBINE:  Propeller turbine is a reaction turbine suitable for low head and large quantity of water. OIL SUMP SERVO TO TURBINE  A Kaplan turbine is propeller turbine with adjustable MOTOR GENERATOR blades. With the help of adjustable blades, a Kaplan STROKE turbine operates at high efficiency even under part load Fig. ARRANGEMENT OF OIL PRESSURE GOVERNOR condition.  In such turbines, water flows radially inward through These governors having these main parts: regulating gates all rounds the sides and change the (a) Relay cylinder (servomotor) direction of runners to axial flow and causing a reaction (b) Control valve or distribution valve. force which drives the turbine. (c) Actuator or pendulum, driven from turbine main shaft by

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gear or belt. (d) Oil sump (e) Oil pump, driven by belt connected to turbine shaft. (f) A mechanism which supplies oil sump with the relay valve and relay valve with servomotor by oil supply pipes.

WORKING:  Due to oil pressure, the piston of servomotor or relay cylinder moves.  This movement of piston rod is amplified and translated to the controlling device of the turbine.  The distributing valve is actuated by speed responsive elements (actuator is used as speed responsive element which works on flyball mechanism) of the governor and controls the supply of the oil to the cylinders.  Oil pump is used to pressurize the oil.  When the speed of turbine falls, the hands of the actuator shaft descends and causes the main lever to raise the pistons of the distributing valve. Due to this action, oil under pressure would send to one end of the oil cylinder and this would move the piston to one side.  This movement would be transmitted to the controlling device to open the nozzle of the impulse turbine or guide vanes of the reaction turbine.  In other case, when the turbine speed rises, reverse action take place.

1.10 HYDROELECTRIC GENERATOR: Standard hydro generators are three-phase synchronous electrical machines for coupling with hydroelectric turbines - through direct coupling or speed-up gear box.

EXERCISES

1. Write the various factors of selection of site for hydroelectric station. 2. Write a short note on hydroelectric energy. 3. How the hydel plants are classified? Discuss briefly. 4. Discuss about the general layout of a hydroelectric power plant. 5. Classify water turbines and describe them briefly. 6. Write a short note on: (i) Penstock, (ii) governor action, (iii) head race, (iv) tail race, (v) water hammer and surge tank.

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